1. Field of the Invention
The present invention relates to a self-priming centrifugal pump, in particular, a pump with a guiding tube and a set of impeller to expedite the flow of fluid downstream so as to achieve the purpose of draining fluid upward from water supply.
2. Description of Related Art
A centrifugal pump will not move liquid unless it is primed. A pump is said to be "primed" when the pump casing and the suction piping are completely filled with liquid. Units that are located below the liquid level of the suction tank can be primped by merely opening the suction and discharge valves, thereby allowing liquid to flow into the pump by gravity. Conventional centrifugal pumps that are located above the suction level must be primed by some auxiliary means such as a vacuum pump, or a ejector. These means of priming chemical pumps are generally unsatisfactory because of the corrosive nature of the liquids being handled. Foot valves are sometimes used on the lower end of the suction line so that it is possible to fill the pump and piping with liquid from an outside source; but this method demands an elevated tank to store the priming liquid. All of these systems require someone to be present to operate the auxiliary equipment initially, and to reprime the pump should it become air-bound during operation.
The self-priming pump is one answer to the above problems. It primes itself, it will reprime if it becomes air bound during operation, and does not require constant attention during operation. However, every time when the self-priming pump starts to move liquid from the supply, air within the piping will slow down the velocity of priming, and the duration of priming the pump will therefore be prolonged and the efficiency reduced, until the air within the piping is fully expelled and there is nothing but liquid within the piping.
The present invention aims to provide an improved self-priming centrifugal pump to obviate or diminish the aforementioned problems.
The self-priming centrifugal pump of the invention has a recirculation tube and an extra set of impellers through which the lifting of air within the piping will be expedited and the liquid returned back to the pump is not only by gravity, but also by the centrifugal effect created by the extra impeller.
Furthermore, a secondary objective of the invention is that a plurality of through holes are provided to the periphery of the seat which has an opening defined to receive an axle and returned liquid therethrough, thereby increasing the speed of liquid returning to the pump.